Remove Individual Data Type Caps in Per-shard Buffering for Remote Write (#8921)

* Moved everything to nPending buffer

Signed-off-by: Levi Harrison <git@leviharrison.dev>

* Simplify exemplar capacity addition

Signed-off-by: Levi Harrison <git@leviharrison.dev>

* Added pre-allocation

Signed-off-by: Levi Harrison <git@leviharrison.dev>

* Don't allocate if not sending exemplars

Signed-off-by: Levi Harrison <git@leviharrison.dev>

storage/remote/queue_manager.go

@@ -1038,23 +1038,21 @@ func (s *shards) runShard(ctx context.Context, shardID int, queue chan interface
 	// If we have fewer samples than that, flush them out after a deadline anyways.
 	var (
 		max                                          = s.qm.cfg.MaxSamplesPerSend
-		// Rough estimate, 1% of active series will contain an exemplar on each scrape.
-		// TODO(cstyan): Casting this many times smells, also we could get index out of bounds issues here.
-		maxExemplars                                 = int(math.Max(1, float64(max/10)))
 		nPending, nPendingSamples, nPendingExemplars = 0, 0, 0
-		sampleBuffer                                 = allocateSampleBuffer(max)
 
 		buf []byte
-		pendingData    []prompb.TimeSeries
-		exemplarBuffer [][]prompb.Exemplar
 	)
-	totalPending := max
 	if s.qm.sendExemplars {
-		exemplarBuffer = allocateExemplarBuffer(maxExemplars)
+		max += int(float64(max) * 0.1)
-		totalPending += maxExemplars
 	}
 
-	pendingData = make([]prompb.TimeSeries, totalPending)
+	var pendingData = make([]prompb.TimeSeries, max)
+	for i := range pendingData {
+		pendingData[i].Samples = []prompb.Sample{{}}
+		if s.qm.sendExemplars {
+			pendingData[i].Exemplars = []prompb.Exemplar{{}}
+		}
+	}
 
 	timer := time.NewTimer(time.Duration(s.qm.cfg.BatchSendDeadline))
 	stop := func() {
@@ -1094,28 +1092,28 @@ func (s *shards) runShard(ctx context.Context, shardID int, queue chan interface
 				return
 			}
 
+			pendingData[nPending].Samples = pendingData[nPending].Samples[:0]
+			if s.qm.sendExemplars {
+				pendingData[nPending].Exemplars = pendingData[nPending].Exemplars[:0]
+			}
 			// Number of pending samples is limited by the fact that sendSamples (via sendSamplesWithBackoff)
 			// retries endlessly, so once we reach max samples, if we can never send to the endpoint we'll
 			// stop reading from the queue. This makes it safe to reference pendingSamples by index.
 			switch d := sample.(type) {
 			case writeSample:
-				sampleBuffer[nPendingSamples][0] = d.sample
 				pendingData[nPending].Labels = labelsToLabelsProto(d.seriesLabels, pendingData[nPending].Labels)
-				pendingData[nPending].Samples = sampleBuffer[nPendingSamples]
+				pendingData[nPending].Samples = append(pendingData[nPending].Samples, d.sample)
-				pendingData[nPending].Exemplars = nil
 				nPendingSamples++
 				nPending++
 
 			case writeExemplar:
-				exemplarBuffer[nPendingExemplars][0] = d.exemplar
 				pendingData[nPending].Labels = labelsToLabelsProto(d.seriesLabels, pendingData[nPending].Labels)
-				pendingData[nPending].Samples = nil
+				pendingData[nPending].Exemplars = append(pendingData[nPending].Exemplars, d.exemplar)
-				pendingData[nPending].Exemplars = exemplarBuffer[nPendingExemplars]
 				nPendingExemplars++
 				nPending++
 			}
 
-			if nPendingSamples >= max || nPendingExemplars >= maxExemplars {
+			if nPending >= max {
 				s.sendSamples(ctx, pendingData[:nPending], nPendingSamples, nPendingExemplars, &buf)
 				s.qm.metrics.pendingSamples.Sub(float64(nPendingSamples))
 				s.qm.metrics.pendingExemplars.Sub(float64(nPendingExemplars))
@@ -1298,19 +1296,3 @@ func buildWriteRequest(samples []prompb.TimeSeries, metadata []prompb.MetricMeta
 	compressed := snappy.Encode(buf, data)
 	return compressed, highest, nil
 }
-
-func allocateSampleBuffer(capacity int) [][]prompb.Sample {
-	buf := make([][]prompb.Sample, capacity)
-	for i := range buf {
-		buf[i] = []prompb.Sample{{}}
-	}
-	return buf
-}
-
-func allocateExemplarBuffer(capacity int) [][]prompb.Exemplar {
-	buf := make([][]prompb.Exemplar, capacity)
-	for i := range buf {
-		buf[i] = []prompb.Exemplar{{}}
-	}
-	return buf
-}